Can two people with brown eyes, black hair and olive skin have a child with blue eyes, blonde hair and fair skin?

It's possible for them to have a child with a completely different phenotype than themselves but the odds of it actually happening are probably low. You would have to look at the parents' genetics to know if there's any history or allele for those traits.

It is possible, but very rare.

The most likely cause of such a thing would be a form of albinism, though it is also possible, if both parents carried such recessive traits, for them to all appear in the child. However, the odds of a child getting only recessive appearance genes and as such looking entirely different from their parents are extraordinarily slim.